How do I render Glowing text effect
The compositor only starts to process the image once the rendering is completed or in case you have activate Auto Render once you change the node configuration. 

There is a small error in your compositing nodes, in order to see the result in the image editor you have to connect the Image output socket of the Glare node to the Composite node.



Once this adjustment has been made, you can render the image from start to finish. The result of the compositing can be viewed in the image editor if you switch from Render Layer to Composite in the dropdown next to the slots.